It is well known that recorder/player units have a serious propensity to be damaged or the magnetic tape used therein to be destroyed, as well as some parts of their mechanism such as the rotating magnetic head assembly when the latter or more precisely the drum of the assembly has its very smooth surface covered even slightly with a liquid substance such as condensation, or cleaning liquid (i.e. alcohol).
This liquid substance once in contact with the magnetic tape, which is wrapped around the rotating drum for record or playback purposes, causes an almost instantaneous sticking of the tape on the rotating drum which results in the unwinding of the tape at the rotational speed of the drum which is in the order of 1500 to 1800 rotations per minute in a video or digital recorder.
Owing to the size of the diameters of these rotating parts (from 50 to 100 millimeters) it is easy to understand that in fractions of seconds, a significant length of the magnetic tape is wrapped around the drum. This produces the following drawbacks: the magnetic tape is unwound outside the cassette and around the different parts of the mechanism and thereafter cannot be rewound in the cassette; the unit must be brought to a service center to be fixed; the magnetic heads, which are extremely sensitive parts protruding from the drum periphery of a few microns, are generally damaged by the magnetic tape entangled around the drum; the magnetic tape even if not torn apart is so damaged that the recordings become useless and are lost.
These phenomena of condensation and dew, noticeable for home video recorders when they undergo sudden changes of temperature (outside/inside a home) are frequently encountered in the case of portable video units which are either connected to a camera or incorporate such a camera. Very frequently these units undergo sudden and large changes of climate, temperature, humidity such as, for instance, when going inside or outside rooms or vehicles.
In the case of portable camera/recorder units when they undergo sudden changes of temperature, as when they are carried into a warm, humid inside environment from outside (cold), for example, moisture will condense on parts such as the rotating magnetic head. Portable video units are frequently equipped with a "dew detector" which indicates by means of a warning lamp, that it is advisable not to operate the video unit and the warning lamp remains "on" as long as the condensation nearby the video head has not returned to an acceptable level, when the detector then switches off the warning lamp.
As can be understood if such a detector warns the user not to operate the video unit to avoid damaging the video head as well as the tape and other components of the unit, it does not bring any solution to the long delay, generally between 15 and 30 minutes, before the video unit becomes dry enough for the user to operate the unit.
Such a waiting period can be very annoying as usually the user desires to operate the portable video unit without delay.
This sensitivity to sudden changes of temperature, dew conditions, and climate conditions limits the convenience of use of portable units.
Furthermore, for all video units it is recommended to wait for about 15 minutes before inserting a magnetic tape after the use of a cleaning cassette involving the use of a liquid (i.e. alcohol), which is most efficient to clean the heads.
U.S. Pat. No. 4,635,156, commonly assigned, describes such a cleaning cassette in which the problem of delay before the video unit may be used is partly solved by intermittently wetting the tape.
It can be understood, therefore, that it would be important to avoid the above-described problems, in order to protect the magnetic tapes as well as the video recorders/player units and particularly, their most sensitive parts (heads, drum) and allow as much as possible use without delay of portable units.